The chief objective of this contract is to procure the services of a laboratory to perform a particular immunometric assay of human chorionic gonadotropin (hCG) in urine. The assay is described under "Requirements" below. The contractor must also explore methods for refining the assay and develop new assays for hCG and closely related molecules as may be required. Such assays will be used in support of epidemiologic field studies of fertility and early pregnancy loss being carried out by the Epidemiology Branch. Biometry and Risk Assessment Program. National Institute of Environmental Health Sciences.